linux-kernel - Re: [PATCH v1 07/11] fs/proc/vmcore: introduce PROC_VMCORE_DEVICE_RAM to detect device RAM ranges in 2nd kernel

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Message-ID: <Zz22ZidsMqkafYeg@MiWiFi-R3L-srv>
Date: Wed, 20 Nov 2024 18:13:58 +0800
From: Baoquan He <bhe@...hat.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
	kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kexec@...ts.infradead.org, Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
	Thomas Huth <thuth@...hat.com>, Cornelia Huck <cohuck@...hat.com>,
	Janosch Frank <frankja@...ux.ibm.com>,
	Claudio Imbrenda <imbrenda@...ux.ibm.com>,
	Eric Farman <farman@...ux.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1 07/11] fs/proc/vmcore: introduce
 PROC_VMCORE_DEVICE_RAM to detect device RAM ranges in 2nd kernel

On 10/25/24 at 05:11pm, David Hildenbrand wrote:
> s390 allocates+prepares the elfcore hdr in the dump (2nd) kernel, not in
> the crashed kernel.
> 
> RAM provided by memory devices such as virtio-mem can only be detected
> using the device driver; when vmcore_init() is called, these device
> drivers are usually not loaded yet, or the devices did not get probed
> yet. Consequently, on s390 these RAM ranges will not be included in
> the crash dump, which makes the dump partially corrupt and is
> unfortunate.
> 
> Instead of deferring the vmcore_init() call, to an (unclear?) later point,
> let's reuse the vmcore_cb infrastructure to obtain device RAM ranges as
> the device drivers probe the device and get access to this information.
> 
> Then, we'll add these ranges to the vmcore, adding more PT_LOAD
> entries and updating the offsets+vmcore size.
> 
> Use Kconfig tricks to include this code automatically only if (a) there is
> a device driver compiled that implements the callback
> (PROVIDE_PROC_VMCORE_DEVICE_RAM) and; (b) the architecture actually needs
> this information (NEED_PROC_VMCORE_DEVICE_RAM).
> 
> The current target use case is s390, which only creates an elf64
> elfcore, so focusing on elf64 is sufficient.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  fs/proc/Kconfig            |  25 ++++++
>  fs/proc/vmcore.c           | 156 +++++++++++++++++++++++++++++++++++++
>  include/linux/crash_dump.h |   9 +++
>  3 files changed, 190 insertions(+)
> 
> diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
> index d80a1431ef7b..1e11de5f9380 100644
> --- a/fs/proc/Kconfig
> +++ b/fs/proc/Kconfig
> @@ -61,6 +61,31 @@ config PROC_VMCORE_DEVICE_DUMP
>  	  as ELF notes to /proc/vmcore. You can still disable device
>  	  dump using the kernel command line option 'novmcoredd'.
>  
> +config PROVIDE_PROC_VMCORE_DEVICE_RAM
> +	def_bool n
> +
> +config NEED_PROC_VMCORE_DEVICE_RAM
> +	def_bool n
> +
> +config PROC_VMCORE_DEVICE_RAM
> +	def_bool y
> +	depends on PROC_VMCORE
> +	depends on NEED_PROC_VMCORE_DEVICE_RAM
> +	depends on PROVIDE_PROC_VMCORE_DEVICE_RAM

Kconfig item is always a thing I need learn to master. When I checked
this part, I have to write them down to deliberate. I am wondering if 
below 'simple version' works too and more understandable. Please help
point out what I have missed.

===========simple version======
config PROC_VMCORE_DEVICE_RAM
        def_bool y
        depends on PROC_VMCORE && VIRTIO_MEM
        depends on NEED_PROC_VMCORE_DEVICE_RAM

config S390
        select NEED_PROC_VMCORE_DEVICE_RAM
============


======= config items extracted from this patchset====
config PROVIDE_PROC_VMCORE_DEVICE_RAM
        def_bool n

config NEED_PROC_VMCORE_DEVICE_RAM
        def_bool n

config PROC_VMCORE_DEVICE_RAM
        def_bool y
        depends on PROC_VMCORE
        depends on NEED_PROC_VMCORE_DEVICE_RAM
        depends on PROVIDE_PROC_VMCORE_DEVICE_RAM

config VIRTIO_MEM
	depends on X86_64 || ARM64 || RISCV
         ~~~~~ I don't get why VIRTIO_MEM dones't depend on S390 if
               s390 need PROC_VMCORE_DEVICE_RAM. 
        ......
        select PROVIDE_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE

config S390
        select NEED_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE
=================================================